1. Field of the Invention
This invention relates generally to the field of spacecraft analysis, design, and operation. More specifically, this invention relates to a method and corresponding apparatus for use in planning and execution of operations using sensors mounted on a spacecraft.
2. Background Art
A typical Earth satellite or lunar or interplanetary probe has a number of objects attached to its exterior and protruding from it to varying degrees. Such objects include various types of sensors, communications antennas, thrusters, solar power panels and the like, as well as the frameworks and beams on which such objects may be mounted. Other, unintended protrusions from the spacecraft body can result from such phenomena as the partial separation of shielding material from the outer shell of the spacecraft. Conversely, a previously existing protrusion can be eliminated, as, for example, when a solar panel is lost. In addition, the body of the spacecraft itself may take on a wide variety of shapes that are often irregular.
Thus, depending on how a spacecraft-mounted sensor is attached and oriented, its field of view may be obscured (partially or totally) by the spacecraft and the objects protruding from it. Moreover, depending on the sensor's target, its field of view may be obscured by the central body around which it is orbiting (typically the Earth) or another celestial body, such as the Sun or the Moon.
Thus, an important question in spacecraft operations is the extent to which a sensor with a given assigned target is subject to obscuration at various times during the parent spacecraft's orbit or trajectory. The answer to this question can be useful for planning purposes, since it can provide the basis for selecting the optimal times for certain sensing activities. Knowing the extent to which a sensor's field of view is obscured at different times, one can schedule maneuvers to change the attitude or orbit characteristics of the spacecraft to reduce or eliminate the obscuration. Information on obscuration can also play a role in spacecraft design, since it may be possible to place the various objects on the exterior of the spacecraft in such as way as to reduce or eliminate obscuration of its sensors' fields of view.
A related invention is that disclosed in U.S. Pat. No. 5,864,489 for Method and Apparatus for Determining Exposure of Spacecraft-Mounted Solar Panels to Sun and Determination of Spacecraft Drag, which is incorporated herein by reference in its entirety.
Prior methods for calculation of sensor obscuration are accomplished only by performing complex and time-consuming mathematical operations on extensive data regarding the spacecraft's orbit or trajectory, its attitude, desired times for image capture, and other factors. Moreover, while this process may yield numerical data relating the obscuration level to time, it does not provide an easy and reliable way of modeling the data visually, to facilitate the development of alternative designs to minimize the amount of obscuration.
To overcome the shortcomings of the current approach, a method and apparatus are needed that will yield quick and reliable calculations of the degree of obscuration and, at the same time, allow for visual presentation, analysis, and modeling of the data to facilitate the design of alternatives that minimize obscuration of sensors.